1. Field of the Invention
This invention relates to golf balls having improved flying directionality and driving performances, and more particularly to golf balls each having at least 16 symmetrical axes and containing plural dimples equally and constantly disposed on the outer surface thereof so as not to cross with a great circle corresponding to respective symmetrical axis.
2. Related Art Statement
When designing the arrangement, size, shape and the like of dimples on the spherical surface of the golf ball, it is generally practised to take a regular dodecahedron or a regular icosahedron as a basic shape as disclosed, for example, in British Patent No. 377,354, Japanese Patent laid open No. 49-52,029 and U.S. Pat. Nos. 4,142,727 and 4,560,168. In these conventional techniques, considering a spherical triangle obtained by projecting each of equilateral triangles constituting the regular icosahedron onto a spherical surface inscribed or circumscribed with the regular icosahedron, a great circle is formed about a line segment connecting each vertex or center of the spherical triangle to the center of the sphere as a center axis, while the arrangement, size, shape and so on of dimples in each of the spherical triangles are determined in connection with the great circle passing through the respective spherical triangle.
For instance, if it is intended to form the great circle about a line segment connecting each vertex (P.sub.1) of the spherical triangle to the center of the sphere as a center axis, six great circles or six symmetrical axes corresponding thereto are formed as shown by dotted lines in FIG. 5a. If; it is intended to form the great circle about a line segment connecting the center (P.sub.2) of the spherical triangle to the center of the sphere as a center axis, ten great circles or ten symmetrical axes corresponding thereto are formed as shown by dotted lines in FIG. 5b. In FIGS. 5a and 5b, one line of these dotted lines is used as a parting line in the manufacture of the golf ball.
In general, the golf ball is always necessary to have a parting line in the manufacture of the ball. In order to enhance the aerodynamic isotropy of the spherical face of the ball considering such a restriction, it is desirable that the number of particular great circles regularly existing in the ball is made as large as possible to substantially equalize the lift and drag of the flying golf ball with translational and rotational motions at both sides thereof with respect to the respective great circle irrespective of the striking position and to enhance a probability of rotating the golf ball in the same direction as in the extending direction of the great circle. However, when the great circle is formed about the line segment connecting each vertex or center of the spherical triangle to the center of the sphere as in the conventional technique, the total number of great circles is 10 at maximum, so that it is substantially impossible to form more than 10 great circles. Therefore, the aerodynamic isotropy of the conventional golf ball is low and consequently the flying directionality, driving distance and the like are frequently changed in accordance with the striking position on the golf ball.